The impact of magnesium deficiency on photosynthesis and photoprotection in Spinacia oleracea

Limited magnesium (Mg) supply adversely affects photosynthesis. This is particularly related to the high demand for Mg of key enzymes in the chloroplast, such as the photosystems, the ATP synthase and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The accepted critical Mg concentrations for yield and dry matter (DM) are 1.5-3.5 mg Mg g(-1) DM. Earlier studies on Mg deficiency indicated that carbon fixation by Rubisco is severely affected in various plant species, whereas the impact of Mg scarcity on light reactions and photoprotective mechanisms is quite variable. The latter could be related to species-specific differences in the general high light-sensitivity of photosynthetic light reactions. To test this hypothesis, we studied the impact of Mg deficiency in spinach (Spinacia oleracea) plants, which are known to be rather high light resistant. S. oleracea seeds were grown hydroponically under four Mg treatments (1 (control), 0.05, 0.025 and 0.015 mM) and the impact of Mg deficiency on CO2 assimilation, photosynthetic light reactions and photoprotection was determined. Our results show that the photosynthetic efficiency and the overall light stress response were not altered under Mg deficiency, whereas the CO2 assimilation as well as leaf and root Mg concentrations were significantly reduced.